Conventional roof coverings for sloped roofs include asphalt shingles wooden shake shingles, sheet metal, slate, clay and concrete tile. Sheet metal, clay and slate are advantageous because of their high weatherability. Various parts of the world have local or regional architectural preferences for the appearance of the roof. In Europe, clay tile is generally preferred over the relatively flat looking asphalt shingle. Tastes in the U.S. vary, with the western and southwestern part of the U.S. preferring clay tile or wooden shake shingles instead of asphalt shingles.
One of the problems with clay tile and slate roofs is that the clay and slate tiles require significant labor to apply. The asphalt or wood shingles are nailable and are simply nailed to a roof deck in courses, usually from the bottom or cave to the top or ridge of the roof. Clay, concrete and slate tiles are heavier than asphalt shingles, and require more support to hold up the roof. Clay and slate tiles are inherently fragile, and suffer much breakage during shipping and installation. These materials are fragile even after installation on the roof, and can be damaged by foot traffic on the roof. Because of the breakage, high labor requirements, high material costs and extra support required for clay and slate tiles, the installed cost of clay and slate tiles greatly exceeds that of asphalt shingles.
Wooden shake shingles are generally flat boards, usually of cedar or other coniferous trees. The wooden shakes are nailed in courses on the roof deck, with the exposed or tab portions of the shingles of a subsequent course being laid over the headlap portions of the previous course of shingles. The shingles are cut so that the wood grain runs up the slope of the roof for an aesthetically pleasing appearance. The cutting of the wood, and the subsequent weathering of the shingles after installation on the roof create grooves and ridges running in the direction of the wood grain. A disadvantage of wooden shake shingles is that they absorb moisture and swell. Therefore, they must be applied in a spaced-apart arrangement to allow room for expansion. Because of the propensity of wooden shake shingles to absorb water, they tend to curl and not remain flat on the roof.
One of the desirable attributes of any roofing material is to be able to resist fires. This is particularly true in regions having a hot and dry climate, although fire resistance is desirable everywhere. A particularly important aspect of fire resistance is the ability of the roofing material to prevent a fire, or a similar source of heat such as a burning ember, from burning through the roofing material to thereby expose the roof deck or interior of the building to the fire. Metal roofs and clay and tile roofs have inherent advantages in fire resistance over wood shake shingle roofs. Asphalt shingles contain greater than 60 percent filler of finely ground inorganic particulate matter, such as limestone, and therefore are sufficiently fire resistant to obtain a Class A fire rating when measured by appropriate tests. Wooden shake shingles, even when treated with a fire retardant material, are not generally fire resistant and cannot achieve a Class A fire rating. Wooden shake shingles are particularly prone to failing the fire tests (absent fireproofing underlayments) because the shingles cannot be placed with side edges abutting, and the gaps between adjacent shingles contribute to the failure of the shake shingles to pass the fire tests.
Attempts have been made in the past to make cement, synthetic or plastic shingles or tiles to replicate the aesthetically pleasing look of wooden shake roof or tile roofs. Various experiments have been tried to make reinforced cement shingles or tiles. Weatherability, undesirable absorption of water, and long term stability of color can be a problem. Likewise, synthetic or plastic shingles or tiles have not been successful in replacing traditional roofing materials. The plastic material is generally too expensive in material costs, and traditional plastics do not weather well when exposed to sunlight in a roof application for extended periods of time. Further, some plastic materials lack fire resistant qualities.
A roof made from improved composite shingles of organic resinous material and mineral filler material is disclosed in U.S. Pat. No. 5,615,523 to Wells et al. The composite shingle is molded with integrally formed ribs on the underside for structural strength. This composite shingle has a headlap portion, and a tab portion that is normally exposed on the roof. Two nailing strips at the upper and lower ends of the headlap portion of the shingle contain ridges that serve as a nailing indicator for the roofer. Also, U.S. Pat. No. 5,711,126 to Wells discloses an angled composite roofing shingle suitable for use on hip and ridge roof portions, and having mating longitudinal edge surfaces to enable the shingle to cover and conform to the ridge line.
It would be desirable to have a composite shingle which would provide improved nailability over those shingles previously known. The ideal composite shingle would enable the shingle installer to nail the shingle to the roof while avoiding driving the nail through a rib, and without causing a substantial portion of the shingle to break off at the point where the nail is placed. A clean, secure nailing of the shingle to the roof is important to avoid potential sources of leaks and to provide good resistance to wind uplift. The ideal shingle would be easy to manufacture and would have an aesthetically pleasing appearance, such as the appearance of a wooden shake shingle or of a natural slate roof.